Screw connection

ABSTRACT

A screw connection, which is intended in particular for plastic members comprises a screw and an insert member which is to be nonrotatably fitted into one of the components involved in the connection and which receives the screwthread of the screw in an axial passage. In accordance with the invention the axial passage of the insert member is of a smooth-walled, that is to say screwthread-free, configuration and the screw has a screwthread, which cuts or grooves the female screwthread of the insert member. The screw, like the insert, can comprise an aluminum alloy, in which case however the alloy of the screw is of a substantially greater hardness than that of the insert member.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention concerns a screw connection, in particular for plasticmembers, comprising a screw and an insert member, which is to benon-rotatably fitted into one of the components involved in theconnection and which receives the screwthread of the screw in an axialpassage.

2. Description of the Related Art

Screw connections of that kind are known, in the form of so-calledmicro-screw arrangements for small and more specifically thin-walledplastic members. Because these connections are frequently not capable ofwithstanding the forces which occur when screwing in the co-operatingscrewthread of self-tapping screws, the state of the art involves usinginsert members which, in the operation of injection molding of theplastic component, have plastic material injected therearound (referredto as inlays), or which are subsequently embedded hot into the(thermoplastic) plastic member or by means of ultrasound (referred to asinserts). These known insert members comprise brass and are produced inthe form of turned components with a female screwthread in the passageand an outer knurling or the like for the purposes of increasing theirresistance to rotation in the embedded condition. A metric steel screwis used as the screw. This known screw connection not only requiresrelatively high manufacturing costs but it is also high in weight, whichis undesirable in many situations of use, for example in the case ofmobile telephones. Furthermore the necessary tolerances of pre-cutscrewthreads reduce the security of the screw connection against comingloose of its own accord, in particular when dynamic loadings areinvolved; in addition to this, there is also the loss of prestressingforce as a result of fluctuating temperatures because of the differentcoefficients of thermal expansion of the materials involved.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

The drawing illustrates the invention by means of an embodiment. In thedrawing:

FIGS. 1 to 6 show various forms of the insert member in cross-sectionand the respective view A;

FIGS. 7 and 8 show the insert members of FIGS. 2 and 4 in the installedcondition; and

FIGS. 9 and 10 show fixing of a flat profile member to a componentbefore and after a screw is screwed into the insert member.

BRIEF SUMMARY OF THE INVENTION

Aspects include a screw connection for plastic members. Aspects furtherinclude a screw and an insert member, which is to be non-rotatablyfitted into one of the components involved in the connection and whichreceives the screwthread of the screw in an axial passage. Aspectsfurther include the insert member being an aluminum alloy. Aspectsfurther include an axial passage of the insert member being of asmooth-walled (screwthread-free) configuration. Aspects further includethe screw being an aluminum alloy of a substantially greater hardnessthan the alloy of the insert member. Aspects further include the screwhaving a screwthread which cuts or grooves the female screwthread of theinsert member.

For a better understanding of the present invention, preferredembodiments thereof are now described, purely to provide non-limitingexamples, with reference to the attached drawings, wherein:

DETAILED DESCRIPTION OF THE INVENTION

The object of the present invention, more specifically for purposes ofuse of the kind referred to hereinbefore, is to provide a screwconnection, which is cheaper to produce and at the same timeoperationally reliable and secure.

Based on the state of the art set forth in the opening part of thisspecification, the invention provides that the axial passage of theinsert member is of a smooth-wall (screwthread-free) configuration andthe screw has a screwthread which is self-cutting or self-grooving forthe female screwthread of the insert member. Such an insert member issimpler and cheaper to produce than a turned component, morespecifically for example by extrusion, but on the other hand it iscapable of withstanding the forces which occur when the femalescrewthread is being grooved or cut in the passage by means of theappropriately designed screw, without the plastic component whichreceives the insert member suffering damage.

This also constitutes the particularity of the present use of suchscrews, which are extensively known per se and which, by virtue of theirappropriate configuration, themselves cut or groove the counterpartscrewthread in the other component involved in the connection. Hitherto,such screws were used only where there was no need for a specificadditional counterpart component involved in the connection, but thescrew is screwed directly (after a pilot bore has been formed) into thecomponent to be secured or a component holding same.

The diameter of the screwthread-free passage does not have to remain thesame over the axial length thereof, but can decrease from one end to theother. It is also possible for the passage to be of a cross-sectionalshape which differs from a circle, for example it may be of anelliptical cross-section or a round cross-section with projections whichextend in the form of ribs in parallel relationship to the axis alongthe wall of the passage so that the screwthread produced in the inset islimited to those ribs, but the operation of forming the screwthread ismade easier.

It has proven to be advantageous from the point of view of theengineering procedures involved in manufacture and use for the insertmember to be made from aluminum, while a particular advantage which isnot limited to the present situation of use is enjoyed if the screw alsocomprises an aluminum alloy of substantially greater hardness than thatof the insert member. Preferred for the insert member is an aluminumalloy which cannot be age-hardened or which is naturally hard or whichcan be age-hardened in the cold condition, of a hardness<90 HB, whilethe screw is made from an aluminum alloy which can be age-hardened inthe hot condition, of a hardness>140 HB. If tensile strength Rm is takenas the criterion, then that of the screw should be>450 Mpa (N/mm²),while Rm<300 N/mm² should be observed for the insert member. Inparticular an AlMg-alloy or an AlMgSi-alloy falls to be considered forthe insert member, and an AlZnMgCu-alloy is considered for the screw.

Besides the saving in weight in relation to the above-describedconventional pairing by a factor of 3 and besides a highly effectiveself-locking action in respect of the screwthread combination by virtueof the play-free co-operation of the screw and the insert member, thealuminum pairing affords the additional advantage of a low level oflosses in respect of prestressing force, in the event of a fluctuatingthermal load, because the coefficients of thermal expansion of thecomponents involved in the connection are similar; in addition, theseinvolve antimagnetic connection components.

The insert member which is shown in FIG. 1 and which is generallyidentified by reference numeral 1 has a passage 2, which is cylindrical,that is to say circular in cross-section. Provided on its outside, atone end thereof, is a cylindrical collar 3 while over the remainder ofits length, that is to say in the region 4, its outside contour has incross-section an external hexagonal-round profile with ribs 5 andgrooves 6.

The insert member 1 shown in FIG. 2 also has a cylindrical passage 2which at one end however is enlarged over a short part of its length toform a recess 2 a. Provided on the outside at the other end is acylindrical portion 3 while formed in the region 4 is a multi-toothprofile with points 7 and troughs 8.

The passage 2 of the insert member 1 shown in FIG. 3 is closed at itsone end by an end portion 9 so that the passage 2 is in the form of ablind hole. The blind hole is hexagonal in cross-section and in itscross-section the outside surface 10 of the insert member 1 is shaped toafford a multi-tooth profile with points 7 a and troughs 8 a.

In the case of the insert member 1 shown in FIG. 4, the passage 2 iselliptical in cross-section and tapers from one end to the other, in thescrewing-in direction. On the outside, the transverse dimension remainsthe same over the length of the insert member and is shaped to afford amulti-tooth profile with points 7 and troughs 8.

The insert member 1 shown in FIG. 5 has a passage 2, which incross-section involves a contour in the configuration of a roundedhexagon, with ribs 11 and grooves 12. The transverse dimension of thepassage 2 is the same over the length of the insert member 1 while itsoutside surface 10—in the screwing-in direction—is enlarged from one endto the other and is in the form of a multi-tooth profile with points 7 aand troughs 8 a.

The transverse dimensions of the insert member 1 shown in FIG. 6 remainthe same over its length, but its passage 2 is closed at one end by anend portion 9. Moreover the passage 2 is of a trilobal cross-sectionwhile the outside contour 10 is in the form of a rounded outside hexagonprofile with ribs 5 and grooves 6.

FIG. 7 shows the insert member of FIG. 2 in the condition of beinginstalled in a component 20, more specifically in such a way that theend of the insert member 1, which is provided with the recess 2 a,terminates flush with the surface 21 of the component 20.

FIG. 8 shows a similar condition of installation for the insert member 1shown in FIG. 4, more specifically in such a way that the end of theinsert member with the larger diameter of the passage 2 terminates flushwith the surface 21 of the component 20.

FIGS. 9 and 10 show the fixing of a flat profile member 22 to thecomponent 20 by means of the insert member 1, which is fixed therein,and a screw 23. When the screw 23 is screwed into the insert member 1through the hole 24, it cuts or channels in the passage 2 in the insertmember 1 a screwthread which corresponds to the screwthread 25 of thescrew 23, and finally with its head 26 clamps the flat profile member 22fast on the component 20.

All of the above U.S. patents, U.S. patent application publications,U.S. patent applications, foreign patents, foreign patent applicationsand non-patent publications referred to in this specification and/orlisted in the Application Data Sheet, are incorporated herein byreference, in their entirety.

From the foregoing it will be appreciated that, although specificembodiments of the invention have been described herein for purposes ofillustration, various modifications may be made without deviating fromthe spirit and scope of the invention. Accordingly, the invention is notlimited except as by the appended claims.

What is claimed is:
 1. A screw connection for plastic members, the screwconnection comprising: a screw having a screwthread so dimensioned tocut or groove complimentary screwthreads and being of an aluminum alloyhaving a first hardness; and an insert member of an aluminum alloy of asecond hardness substantially less than the first hardness and so shapedto be non-rotatably fitted into one of the plastic members, the insertmember having an axial passage with a smooth-walled configuration toreceive the complimentary screwthread of the screw.
 2. The screwconnection according to claim 1 characterized in that the insert membercomprises a naturally hard or cold age-hardenable aluminum alloy of ahardness less than 90 HB and the screw comprises a hot age-hardenablealuminum alloy of a hardness greater than 140 HB.
 3. The screwconnection according to claim 1 characterized in that the insert membercomprises an AlMg— or AlMgSi-alloy and the screw comprises anAlZnMgCu-alloy.
 4. The screw connection according to claim 1characterized in that the cross-section of the axial passage is of anon-round configuration.
 5. The screw connection according to claim 1characterized in that the cross-section of the axial passage decreasesin the longitudinal direction.
 6. The screw connection according toclaim 1 characterized in that the outside cross-section of the insertmember has axially extending radial projections.
 7. The screw connectionaccording to claim 1 characterized in that the outside cross-section ofthe insert member enlarges in the longitudinal direction.
 8. The screwconnection according to claim 1 characterized in that the insert memberis an extrusion workpiece.
 9. A glueless screw connection for plasticmembers, the screw connection comprising: a screw formed of an aluminumalloy having a first hardness, and having a screwthread so dimensionedto cut or groove complimentary screwthreads; and an insert formed of analuminum alloy of a second hardness, substantially less than the firsthardness, and so shaped to be non-rotatably fitted into one of theplastic members, the insert having an axial passage having alongitudinal dimension and having a smooth-walled configuration toreceive the complimentary screwthread of the screw and to secure theinsert in the plastic member without need of gluing, by expansion of theinsert as the screw is initially screwed into the insert along thelongitudinal dimension.
 10. The screw connection of claim 9 wherein theaxial passage has a cross-section perpendicular to the longitudinaldimension and the cross-section of the axial passage is of a non-roundconfiguration.
 11. The screw connection of 9 wherein the axial passagehas cross-section perpendicular to the longitudinal dimension, and anentrance for insertion of the screw, and the cross-section of the axialpassage decreases with position along the longitudinal direction fromthe entrance.
 12. The screw connection of claim 9 wherein the insert hasan outer surface having axially extending radial projections.
 13. Thescrew connection of claim 9 wherein the insert has an entrance forinsertion of the screw and an external diameter that increases withposition along the longitudinal direction from the entrance.
 14. Thescrew connection of claim 9 wherein the insert is an extrusionworkpiece.
 15. The screw connection of claim 9 wherein the insertcomprises a naturally hard or cold age-hardenable to aluminum alloy of ahardness less than 90 HB in the screw comprises a hot age-hardenablealuminum alloy of a hardness greater than 140 HB.
 16. The screwconnection of claim 15 wherein the insert comprises analuminum-magnesium or aluminum-magnesium-silicon alloy and screwcomprises an aluminum-zinc-magnesium-copper alloy.
 17. A fastener,comprising: an insert formed of an aluminum alloy having a firsthardness and shaped to be non-rotatably fitted into a plastic substrate;an axial passage formed in the insert with smooth walls, longitudinally,and configured to receive a screw formed of an aluminum alloy of asecond hardness, substantially greater than the first hardness, thepassage further configured to be tapped by the screw upon introductionof the screw into the axial passage.
 18. The fastener of claim 17wherein the axial passage is cylindrical and smooth, laterally.
 19. Thefastener of claim 17 wherein the axial passage is longitudinally ribbed.20. The fastener of claim 17 wherein the axial passage is oval in across section taken perpendicular to the longitudinal axis.